[WiP] Fix trial expiration

Separating plan_level from community to a new table for the sake of saving some data about when communities have changed their plan levels.
Is there a reason to extract it?

Since this variable is created in every view and ensure_is_admin is used only outside of application_controller 
=> I think I could just change the 'unless' condition of ensure_is_admin to check just this variable (@is_current_community_admin)?